1. Field of the Invention
The invention relates to means for producing optimized cooler waveforms to improve the coefficient of performance of cryogenic coolers, and especially to using linear motor drive means for producing both the compression waves in the working gas and regenerator-displacer movement in proper wave shapes and phased relationship.
2. Description of the Prior Art
Cryogenic coolers that operate at liquid nitrogen temperatures suffer from poor reliability. Most of the reliability problems are the result of working fluid gas contamination and of wearout of the moving parts. Linearly driven compressor pistons and regenerator-displacers can help solve the poor reliability problem, while providing improvements in performance at reduced fabrication costs. cl SUMMARY OF THE INVENTION
The present invention relates to linear motor drive means for producing optimized waveforms in a closed cycle cryogenic cooler in which the cooler is remote to a compressor. The compressor piston and the cooler regenerator-displacer are driven by separate linear motors. The motors are resonant with each other to provide maximum coefficient of performance in which the compressor waves are produced about 90.degree. ahead of the cooler. The compressor provides pressure waves by way of a cooling gas feed line to the regenerator-displacer of a cold finger of the cooler. The displacer waves are produced in like motion but with a delay of about 90.degree..
The compressor is activated by a motor control means switching in the compressor linear motor wherein the compressor piston is attached to the motor. The compressor is operated near its resonant frequency. The following advantages are realized. Clearance seals may be used instead of friction seals because of the elimination of side forces. Elements that are eliminated include the ball bearings, the flywheel, the connecting rod, the crankshaft and any lubrication. The size and weight are greatly reduced and the acoustic noise generation is suppressed because of the reduction of metal to metal contact. Reliability is increased due to the elimination of the lubricants and bearings. It should be noted that lubricants are a main source of gaseous and particulate contamination. The coefficient of performance is improved because the compressor linear motor can produce a selected optimum waveform for the compressor piston to follow.
The remote cold finger portion of the cooler is the cooling surface. The displacer in the cold finger is operated by a cooler linear motor. Advantages of the cooler portion are as follows. The reliability of the cold finger is greatly enhanced because the cooler linear motor does not have radial forces that causes wearout. An improvement in the coefficient of performance is realized because the cooler linear motor can generate an optimum waveform for the displacer to follow.
A motor control means is used to establish the proper waveshapes and phasing somewhere about the 90.degree. advance for the compressor linear motor ahead of the cooler linear motor. This fine tuned phasing is performed while monitoring the actual cooling of the cold finger. The motor control means is set to phase the motors accordingly.